In response to the recent movement toward energy conservation, the field of illumination undergoes some changes. Replacing conventionally used incandescent lamps, low-pressure mercury discharge lamps have been increasingly used owing to their high lamp efficiencies and long lives. A compact self-ballasted fluorescent lamp is one example of such low-pressure mercury discharge lamps.
Such a compact self-ballasted fluorescent lamp (hereinafter, referred to simply as a “lamp”) is composed generally of an arc tube, a lighting unit for operating the arc tube, and a case for holding the arc tube and housing the lighting unit therein. In addition, a base is connected to one end of the case, for attachment of the lamp to a socket of an illumination fixture and for drawing a power from a commercial power supply.
The lighting unit is of a so-called inverter type. In one example, the lighting unit is generally composed of: a rectifier circuit module having a diode bridge element; an inverter circuit module having a pair of FET elements; and a resonance circuit module having a choke coil, a resonance capacitor, and so on.
Especially, since recent high-frequency inverters invert input of a DC power into a high frequency current, it is more common to use a so-called capacitor input system. According to the capacitor input system, the lighting unit is provided, at the output end of the rectifier circuit module, with a smoothing circuit module having a smoothing capacitor for smoothing an electric current rectified by a diode bride element (See for example, JP patent application publication number 2000-77195). Note that when a lighting unit has both a rectifier circuit module and a smoothing circuit module, the two circuit modules are collectively referred to as a “rectifier/smoothing circuit module”.
Some lighting units of the above type is provided with an inrush current limiting resistor at the input end of the rectifier/smoothing circuit module in order to suppress the inrush current drawn by a power supply when it is turned on.